Poly(1,4-butylene terephthalate) resin is widely used in molding compositions due to its many excellent properties, i.e., dimensional stability, strength, solvent resistance, etc. Of growing importance are applications which require that this resin also have good electrical properties. In such applications, the molded parts may be exposed to severe conditions, such as exposure to electrical discharge or to excessive leakage current across a surface. These conditions require not only that the molded part have flame resistance, but also that the molded part have a high degree of resistance to carbonization, i.e., good track resistance, and a high degree of resistance to electrical discharge, i.e., good arc resistance.
It has been a problem that poly(1,4-butylene terephthalate) resin generally has insufficient electrical properties. Polyester resin molding compositions with improved arc resistance are described, for example, in U.S. Pat. No. 4,052,356, issued Oct. 4, 1977, to Breitenfellner, et al., and assigned to Ciba Geigy A.G. This patent discloses reinforced polybutylene terephthalate compositions containing kaolin from which molded articles having an Arc Resistance of 80-125 sec., ASTM D-495, and a Comparative Tracking Index, ASTM 3638, of 250-275 volts can be obtained. U.S. Pat. No. 4,035,333, issued July 12, 1977 to Kamada, et al., and assigned to Mitsubishi Rayon Co. Ltd., discloses that polybutylene terephthalate molding compositions containing sodium antimonate or a sodium antimonate/antimony trioxide mixture together with talc provide molded articles having improved arc resistance. Japanese Published Patent Application No. 52-58752/1977 discloses flame resistant polyester molding compositions containing mineral fillers and fibrous glass to provide a resin with an improved arc resistance. It has been found that flame retardant polybutylene terephthalate resin compositions filled with approximately 30 to 60 percent by weight of fibrous glass and talc will provide articles molded therefrom with an Arc Resistance of at least 150 sec. and a Comparative Tracking Index of at least 400 volts.
Therefore, it is an object of the present invention to provide poly(1,4-butylene terephthalate) resin molding compositions having improved electrical properties.
It is a further object of the present invention to provide flame retarded poly(1,4-butylene terephthalate) resin molding compositions having improved electrical properties.